The objectives of this research are to improve our understanding of the mechanisms of metal acquisition by microorganisms in the marine environment. Interest in the mechanisms of acquisition of iron (and other metal ions) by oceanic bacteria derives from the unique transition metal ion composition of the ocean and the discrepancy between iron availability and requirements. Iron is a limiting nutrient to marine microorganisms over much of the world's oceans at a concentration of 0.02-1 nM in surface seawater, whereas molybdenum and vanadium are the two most abundant transition metal ions at 100 nM and 20-35 nM, respectively. In the previous grant period the Principal Investigator discovered a new class of self-assembling amphiphilic peptide siderophores, the marinobactins and aquachelins, produced by two phylogenetically distinct genera within the marine gamma proteobacteria. The only siderophores which bear a structural resemblance to the marinobactins and aquachelins are the amphiphilic mycobactin and exochelin siderophores. These siderophores are produced by mycobacteria, such as Mycobacterium tuberculosis, the bacterium causing tuberculosis. Little is known about the molecular mechanism of pathogenesis of M. tuberculosis, however, its capacity to infect the host is closely linked to its ability to acquire iron. The specific aims of the proposed research include I) further characterization of the amphiphilic marine siderophores and the mycobactins, II) further investigations of the Alteromonas luteoviolacea system, the marine bacterium which produces the alterobactin siderophores and III) the isolation and structural characterization of siderophores produced by other oceanic bacteria. These studies are the first part of an investigation into whether the mechanisms of iron acquisition (e.g., siderophore-mediated sequestration of the iron, outer membrane receptor protein recognition of the metal siderophore complex, transport, and metal regulation of these processes, etc.) by marine bacteria differ from terrestrial bacteria.